RDF to ArangoDB (RPT)

Virtualizng ArangoDB as a Triple Store

What is RPT?

The RDF-topology Preserving Transformation (RPT) algorithm preserves the RDF graph structure by transforming each RDF statement into an edge in the Property Graph (PG).

Consider the following RDF Graph:

@prefix ex: <http://example.org/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .

ex:book ex:publish_date "1963-03-22"^^xsd:date .
ex:book ex:pages "100"^^xsd:integer .
ex:book ex:cover 20 .
ex:book ex:index 55 .

RPT converts the triple (ex:book, ex:index, 55) into two nodes (ex:book) and (55), connected by an edge (ex:index). All other triples involving RDF resources, blank nodes, or literal values can be transformed in a similar way so that we obtain the Property Graph below:

RPT Graph

The Algorithm below formalizes the RPT approach. For each triple, create a node for the subject (line 3) and the object (line 5), with an edge connecting them (line 12) - of course avoiding duplicate nodes for the same IRIs.

RPT Algorithm

Now, consider the following RDF-star Graph:

@prefix ex: <http://example.com/> .

<< ex:Mary ex:likes ex:Matt >> ex:certainty 0.5 .
<< ex:Mary ex:age 28 >> ex:certainty 1 .

ArangoRDF’s RPT transformation for RDF-star Graphs is slightly different from the transformation proposed in the paper. In order to preserve the concept of virtualizing ArangoDB as a Triple Store, conversion for RDF-star statements is identical to RDF triples. This is not the case for the RPT transformation proposed in the paper, which proposes to add the ex:certainty 1 as an edge attribute to the edge connecting the nodes ex:Mary and 28. Instead, ArangoRDF’s RPT transformation expresses (..., ex:certainty, 1) as its own edge:

RPT Star Graph

Please Note: The rdflib python package hasn’t yet introduced support for Quoted Triples, so ArangoRDF’s support for RDF-star is based on Triple Reification.

As a result, the RDF-star Graph above can be processed with ArangoRDF as follows:

from rdflib import Graph
from arango import ArangoClient
from arango_rdf import ArangoRDF

data = """
    @prefix ex: <http://example.com/> .
    @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

    # << ex:Mary ex:likes ex:Matt >> ex:certainty 0.5 .
    # << ex:Mary ex:age 28 >> ex:certainty 1 .

    [] a rdf:Statement;
        rdf:subject ex:Mary;
        rdf:predicate ex:likes;
        rdf:object ex:Matt ;
        ex:certainty 0.5 .

    [] a rdf:Statement;
        rdf:subject ex:Mary;
        rdf:predicate ex:age;
        rdf:object 28 ;
        ex:certainty 1 .
"""

rdf_graph = Graph()
rdf_graph.parse(data=data, format="turtle")

db = ArangoClient().db()
adbrdf = ArangoRDF(db)
adbrdf.rdf_to_arangodb_by_rpt(name="DataRPT", rdf_graph=rdf_graph, overwrite_graph=True)

ArangoDB Collection Mapping Process

The ArangoDB Collection Mapping Process is defined as the algorithm used to map RDF Resources to ArangoDB Collections. In RPT, the ArangoDB Collections generated are consistent:

  1. {Name}_URIRef: The Vertex collection for rdflib.term.URIRef resources.

  2. {Name}_BNode: The Vertex collection for rdflib.term.BNode resources.

  3. {Name}_Literal: The Vertex collection for rdflib.term.Literal resources.

  4. {Name}_Statement: The Edge collection for all triples/quads.

Using the python example from above, the RDF Resources of your RDF Graph would be stored under the following ArangoDB Collections:

  1. DataRPT_URIRef

    • ex:Mary

    • ex:Matt

  2. DataRPT_BNode

    • [] (1)

    • [] (2)

  3. DataRPT_Literal

    • 0.5

    • 1

  4. DataRPT_Statement

    • ex:Mary -> ex:likes -> ex:Matt

    • ex:Mary -> ex:age -> 28

    • (ex:Mary -> ex:likes -> ex:Matt) -> ex:certainty -> 0.5

    • (ex:Mary -> ex:age -> 28) -> ex:certainty -> 1

This is the consistent naming scheme for all ArangoRDF RPT transformations. The name of the RDF Graph is used as a prefix for the 3 Vertex Collections and the 1 Edge Collection.

Supported Cases

Note: RDF-to-ArangoDB functionality has been implemented using concepts described in the paper Transforming RDF-star to Property Graphs: A Preliminary Analysis of Transformation Approaches.

The paper presents a systematic list of test cases that transformation approaches need to fulfill. These test cases range from simple RDF Graphs to complex RDF-star Graphs.

ArangoRDF’s RPT interface can be observed here.

View how ArangoRDF’s RPT transformation approach performs on these test cases in Colab.

Cases